On Tue, Jan 08, 2013 at 11:22:39PM +0400, Anton Dergunov wrote:
I have written a draft of an introductory-level tutorial paper about GADTs in Haskell (for submittion to proceedings of the recent LASER summer school) and I would like to seek initial feedback about its content: what information is probably missing? are there any subtle mistakes?
Not exactly the feedback you asked for, but I hope it still can be of some use. As a person with no prior knowledge about GADTs, I found your paper a good introduction. Following proof of correctness of red-black tree insertions turned out to be a little bit of a challenge as type annotations quickly become tangled (made me wondering how one should prove correctness of the proof). I particularly liked how you handle things that are not central to tutorial, like phantom and existential types: you give single-sentence explanation that provides good enough intuition to follow you further. Talking of quick explanations, I would love to see kinds and singleton types explained in the same manner. You tried to explain singleton types at page 13, but I find explanation provided by GHC documentation[1] to be much more clear. As for kinds, it just puzzles me why you use the term but don't explain it. 1. http://hackage.haskell.org/trac/ghc/wiki/TypeNats/Basics The same goes for type families - while I was able to quickly look up definition of singleton types, I failed to comprehend basics of type families by reading Haskell Wiki. I ended up pretending that type families are just type-level functions. I would love to see Yampa optimizations section expanded with more interesting examples. Are there any? Last but not least, a few minor typos and errors I spotted: * at page 8, "Than we need to declare type instances..." should be "Then we need..."; * probably due to excessive editing, parameters to repeatElem at page 13 are in the different order than before; * at page 14, you state:
As in all binary search trees, for a particular node N c l x r values greater than x are stored in left sub-tree (in l) and values less than x are stored in right sub-tree (in r).
But later on, your code contradict that statement by recursing to left sub-tree when x we look for is less than value in the node, and to right sub-tree when x is greater than value in the node. Thank you once again for a nice introduction to GADTs! -- Regards, Alexander Batischev PGP key 356961A20C8BFD03 Fingerprint: CE6C 4307 9348 58E3 FD94 A00F 3569 61A2 0C8B FD03